1. Field of the Invention
This invention relates to a method of manufacturing a hollow fiber and, more particularly, to a method of manufacturing a hollow fiber having favorable selective permeability.
2. Description of the Prior Art
Hollow fibers are widely used in various fields. A method of manufacturing a hollow fiber has been investigated in order to impart various performances to the hollow fibers.
Examples of the successful use of hollow fibers are a hollow-fiber type artificial kidney, a hollow-fiber type module for reverse osmosis, a hollow-fiber type ultrafiltration module and a hollow-fiber type reverse-osmosis condenser.
Artificial kidneys are used for patients suffering from renal failure. Metabolic waste such as urea and uric acid are selectively removed from the blood of a patient by an artificial kidney. A well-balanced ultrafiltrating property or dewatering property with the removal of metabolic waste is required of an artificial kidney.
Hollow fibers are also used for reverse osmosis, for example, for desalting sea water. A good water-flux and rejecting property against salt are required for reverse osmosis. Hollow fiber type modules are also used for treating polluted water from factories and for producing sterile water.
Hollow fiber type reverse osmosis condensers are also used in the food industry for condensing juice. This method is advantageous because it causes a minimum loss of vitamins during the condensation process. Also, because heat is not used in this method, it saves energy.
In using hollow fibers, a fluid to be treated flows through the hollow portions of said fibers. Accordingly, the hollow portion should extend longitudinally through the whole length of each fiber. The membrane of the hollow fiber should not be even partially broken. Further, it is required that the thickness of the membrane of the hollow fiber be uniform over the fiber's whole length and that the diameter of the fiber be as small as possible, thereby to provide sufficient mechanical strength.
A conventional method of manufacturing a hollow fiber comprises extruding a spinning solution (dope) from an annular slit of a double pipe orifice to form a sheath solution, while simultaneously extruding a gaseous or liquid fluid from the inner pipe of the double pipe orifice to form a core fluid. A liquid core fluid is superior to a gaseous core fluid for stable spinning. The core liquids of the prior art can be classified into two categories, to wit: